File photoBENGALURU: Flooded neighbourhoods are a common sight in Bengaluru. That is because the drains outside homes are paved with concrete, which experts say causes rainwater runoff resulting in floods.

In fact, the BBMP is spending Rs 800 crore to construct new storm-water drains and remodel existing ones using reinforced cement concrete (RCC). A team of civil engineering students has now come up with a new type of mix called pervious concrete, which allows rainwater to permeate, reducing flooding and helping groundwater recharge.Students developed a block of pervious concrete using their own mix proportion of water, cement and other aggregates.

In fact, the innovation by CMRIT students won first prize at Srishti 2017, a state-level competition for engineering students. Final year students Nandhini RT, Netravathi O, Danish Akhtar and Manoj GK were mentored by their teacher Preeti Jacob, who specialises in water resources. "Normal concrete is very impermeable. Because of that, we end up wasting precious rainfall. Also, the use of concrete in drains contributes to rising temperature," Nandhini said.

To demonstrate the effectiveness of the pervious concrete, the students ran a laboratory test recreating rainfall conditions. Water was poured on the pervious concrete block and a layer of soil taken from all five locations to study permeability. "During rainfall, if the bed of the stormwater drain is pervious, some water seeps down and the effect of flood is reduced. Use of this pervious concrete in the small drains can reduce flooding by 70%," said Jacob, assistant professor of Civil Engineering at CMRIT.

At Rs 10 a block, this concrete is a cost-effective solution for the city .Municipal commissioner N Manjunath Prasad said he would ask engineers to take a look at the concrete if students approach him."The concern that the use of concrete in drains increases velocity of water is valid. But Bengaluru's drains also carry sewage. If this seeps through, the borewells may get contaminated," Prasad said, justifying the use of concrete in drains.